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Numerical error or case error? Flow in a 3D pipe

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Old   January 30, 2013, 08:10
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Jakub Pola
Join Date: Feb 2011
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stainboy is on a distinguished road
The case for Re = 1 works as expected.
For pressure driven flow I've obtained following results
U_analytical: Umax=6.66e-5m/s U_OF: U_max=6.268e-5m/s which is 94%
DP_analytical: =1.77e-7 m2/s2, DP_OF: 1,77422e-7 m2/s2

Then I've tried higher Re. First one is Re = 10.
Here are analytical results:
Vavg=3.33e-4 m/s , P=1.774e-6 m2/s2 Vmax =6.66e-4 m/s

Results obtained from OF simulations are following:
U_OF_max = 6.423e-4 which is 96% and DP_OF=1.82e-6m^2/s^2

When I've tried Re = 100. Results are much worse.
Analytical solution: Vavg=3.33e-3 m/s , P=1.774e-5 m2/s2 Vmax =6.66e-3 m/s
Solution from OpenFOAM:
U_OF_max = 5.92e-3 m/s DP_OF = =2.343e-5 m2/s2.

Above results were obtained with the mesh mentioned in my previous post. I've simulated Re=100 with mesh with higher resolution and the results are even worse.
Here is the screen of the mesh, and here is the link to velocity profile chart.

Could you please support me, what I'm doing wrong. I expected that results will be closer to analitycal comparing to mesh with less elements.

I can provide anything what is neccessary to perform the simulation.

It was mesh with ~2M elements with boundary layer. The statistics of that mesh are following:

Overall number of cells of each type:
    hexahedra:     0
    prisms:        956496
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    1075964
    polyhedra:     0

Max aspect ratio = 7.03624 OK.
    Minumum face area = 3.13765e-06. Maximum face area = 8.65999e-05.  Face area magnitudes OK.
    Min volume = 2.54999e-09. Max volume = 2.57872e-07.  Total volume = 0.0628124.  Cell volumes OK.
    Mesh non-orthogonality Max: 65.5048 average: 12.0036
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.765097 OK.
    Coupled point location match (average 0) OK.
Thank you in advance for your help.
Best regards,
stainboy is offline   Reply With Quote


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